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Coverage Measurement in the 2010 Census 4 Technical Issues This chapter discusses several issues related to the proposed census coverage measurement (CCM) program for 2010: the sample design for the CCM postenumeration survey (PES), use of logistic regression models, missing data in new coverage error models, matching cases with minimal information, and demographic analysis. On several of these topics the panel offers recommendations for the Census Bureau. SAMPLE DESIGN FOR CENSUS COVERAGE MEASUREMENT The Census Bureau is planning a CCM PES sample of 300,000 housing units, with primary sampling units composed of block clusters (for details, see Fenstermaker, 2005). An important question concerning the census coverage measurement program in 2010 is to what extent can and should the new goal of process improvement be incorporated into the design of the CCM PES. For purposes of CCM design, the United States will be divided into 3.7 million block clusters, and the CCM will select about 10,000 of these, each averaging roughly 30 housing units (for a total of 300,000 housing units). The Census Bureau will use an initial stratification of the 3.7 million block clusters into four types: (a) small, with between 0 and 2 housing units (as determined by the Census Bureau’s Master Address File in 2009), (b) medium, with between 3 and 79 housing units, (c) large, with more than 80 housing units, and (d) block clusters of groups of American Indians on reservations. The current proposed CCM design will allocate
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Coverage Measurement in the 2010 Census a minimum of 1,800 housing units from about 60 medium and large block clusters per state (3,000 block clusters of the 10,000), with the remainder allocated proportionate to state population size. Also, Hawaii is allocated a minimum of 4,500 housing units in the CCM sample (roughly 150 block clusters), and 10,000 housing units (roughly 330 block clusters) are selected of American Indians living on reservations, which are allocated proportionally to the number of American Indians living on reservations in each state. Once the 10,000 block clusters for the CCM are identified, they will be independently listed to determine how many housing units are actually present (since the MAF does not provide a perfect count and also because the MAF will be slightly dated). In particular, for small block clusters, this independent listing will find many of them to have more than two housing units. If the number of housing units for small block clusters is found to be more than 10, current plans are to choose those block clusters into the CCM sample with certainty. Otherwise, the remaining small block clusters will be subsampled. (Plans are to subsample small block clusters with between none and two housing units at the rate of 0.1, those with between three and five housing at the rate of 0.25, and those with between six and nine housing units at the rate of 0.45.) Finally, regarding substate allocations of block clusters, while plans are currently not final, the Census Bureau is likely to include some modest degree of oversampling of block clusters in areas that have a large fraction of people that rent their residences and possibly in areas that have a large fraction of minority residents. The general argument in support of the state allocations for the 2010 CCM PES is that they mimic those for 2000, since the Census Bureau was generally satisfied with the 2000 design of the Accuracy and Coverage Evaluation (A.C.E.) Program in terms of the variance of estimates of net undercoverage for poststrata. (The Census Bureau has no specific variance requirements for the 2010 CCM estimates, because production of adjusted counts is not anticipated.) With respect to substate allocations, the Census Bureau is concerned with increased variances and so intends to refrain from more than a modest amount of oversampling. The Census Bureau examined some alternative specifications for the design of the CCM PES to see if they might have advantages, using simulation studies of both the quality of the resulting net coverage error estimates and the quality of estimates of the number of omissions and erroneous enumerations at the national level and for 64 poststrata (for details, see Fenstermaker, 2005, 2006). Initially, four designs were examined: (1) the design described above—i.e., allocations proportional to total state population, with a minimum of 60 block clusters per state, with Hawaii allocated at least 150 block clusters; (2) as (1) except with
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Coverage Measurement in the 2010 Census Hawaii allocated at least 60 block clusters; (3) allocations to the four census regions to minimize the variance of estimates of erroneous enumerations, and within regions, allocations are proportional to state size; and (4) half of the sample is allocated proportional to the number of housing units within update/leave areas1 and half is allocated proportional to each state’s number of housing units. Through use of simulations, for each design and resulting set of PES samples across simulation replications, national estimates were computed of the rate of erroneous enumerations (and the rates of erroneous enumerations from mail returns, from nonresponse follow-up, and from coverage follow-up), the nonmatch rate, the omission rate, and the net error rate. National estimates of the population were also computed, along with their standard errors. The same analysis was done at the poststratum level. One hundred replications were used for the simulation study. The results supported retention of the design that closely approximated the 2000 A.C.E. design (described above). A subsequent analysis added an additional six proposed sample designs for analysis. The panel supports the overall sample size of 300,000 housing units, which was also endorsed, as part of Recommendation 6.1, by the Panel to Review the 2000 Census (National Research Council, 2004b). Such a design would produce net coverage estimates of similar precision to those of the 2000 A.C.E. The adequacy of the CCM sample size is somewhat supported by the adequacy of the A.C.E. sample size, though the objectives of these surveys have changed and therefore arguments used to support the A.C.E. sample size may no longer be fully relevant. However, such a position is necessary given the current lack of experience estimating the components of census coverage error. Aside from sample size, the selection of a sample design for the CCM in 2010 will involve addressing related but somewhat competing goals, given that there are two overall objectives of the coverage measurement program for 2010. First, there is the primary objective—the measurement and analytic study of components of census coverage errors. Second, there is still the need to be able to measure net coverage error for at least three reasons: (1) to estimate the number of census omissions, (2) to serve the many users who remain interested in assessments of net error at least for states and major demographic groups, and (3) to facilitate comparison with the quality of the 2000 census. To address the first general goal, one would like to target problematic domains—determined using 2000 census data or data from the American Community Survey (ACS) for which there is predicted to be a high fre- 1 These are areas in which the enumerator updates the address list, and, at the same time, drops off a questionnaire to be filled out and returned by mail.
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Coverage Measurement in the 2010 Census quency of various types of census coverage error. (In an optimal design for any individual component, the sampling rate would be proportional to the stratum standard deviation, which is likely to be higher in strata where the particular coverage error is greater.) However, one has to be careful because one also has to have a facility for discovering any unanticipated problems that might appear in areas that were relatively easy to count in 2000. Each census seems to raise relatively novel sources of census coverage error, and at the same time, each census seems to have areas that were hard to count a decade earlier and subsequently are relatively easy to count. Yet the goal of producing high-quality estimates of net coverage error for all states and for all major demographic groups calls for a design that is somewhat less targeted. As with estimation of components of error, the most efficient design for estimation of net coverage error would oversample areas with high rates of omissions or erroneous enumerations. This then allows reducing the sampling weights associated with individual blocks expected to exhibit the most variance in the two components of net error. However, it is especially critical for net error estimation to avoid extreme undersampling in any areas because large sampling weights will quickly inflate variances if associated with blocks having more problems than anticipated. Another way to look at the situation is that there is a modest tension between the need for cross-U.S. reports on net coverage error, and the need for specific analytic studies on possibly problematic processes. So if one had a list of potentially worrisome places where census processes are likely to enumerate certain kinds of housing units with a high frequency of coverage error, those places should be oversampled in the 2010 CCM design. But this should be done while maintaining the ability to produce reliable estimates of net coverage error at some level of geographic and demographic detail. Given this modest tension, the panel believes that the Census Bureau has selected a design that may not sufficiently accommodate the primary goal of measuring and analyzing components of census coverage error. The state allocations of the Census Bureau’s proposed CCM sample design are too oriented toward producing state-level estimates of net undercoverage of comparable quality with the 2000 estimates. Instead, the new purpose of CCM in 2010 should be accommodated by modifying the state allocations of block clusters to include more block clusters from states that are predicted to be harder to count, by including a greater degree of oversampling of substate areas that are likely to be difficult to count (though the latter is clearly dependent on the Census Bureau’s as yet unspecified plans), or both. The analysis carried out by the Census Bureau of 10 sample designs
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Coverage Measurement in the 2010 Census for state allocations is thorough. However, with respect to substate allocations of block clusters, the Census Bureau might consider, in addition to oversampling medium and large block clusters with a high percentage of renters, oversampling block clusters with large percentages of individuals or housing units with other features that might be associated with census coverage error, such as: (1) small multiunit structures, (2) a high percentage of foreign-born residents in 2000, (3) a high percentage of proxy interviews in 2000, (4) a high percentage of whole household imputation in 2000, (5) a high percentage of vacation homes, or (6) recent additions to the housing stock. In addition, as in 2000, the Census Bureau could oversample blocks in which there is a higher chance of geocoding errors or areas in which there was a high percentage of additions through the Local Update of Census Address (LUCA) Program or block canvass adds or deletes.2 It is likely that efforts devoted to modifying substate allocations will be more important than the state allocations, but both deserve attention. In addition to the above general suggestions, the panel has a specific suggestion for the 2010 CCM sample design that provides a reasonable compromise between designs that are focused on estimation of net coverage error and designs that focus on components of census coverage error. We urge the Census Bureau to evaluate a CCM sample design that retains the identical structure of the current census design for a substantial fraction of the sampled units, possibly 60 to 75 percent (by making the obvious change to the sampling rates) and allocates the remaining sample to anticipated problematic regions or block clusters. Such a change would potentially provide a much greater number of census coverage errors to support models examining which factors relate to coverage error. At the same time, allocating the bulk of the sample to a general purpose design would limit the risk of inflated variances for net error estimates associated with finding large errors in unexpected locations. Research on what percentage to use and how this compares with the Census Bureau’s proposed design can be carried out using simulation studies of the type the Census Bureau has already carried out, though it also would be very useful to incorporate some accounting for any differences that are expected to be seen between 2000 and 2010 (possibly based on the ACS). In conducting additional simulations, we propose that the Census 2 In considering characteristics that can serve as the basis for oversampling, it is important to stress that even if some problematic circumstances are identified, it will generally be the case that very little individual household-level information could be used as the basis for oversampling since such information would have to be available on the MAF. However, area-wide frequencies of the same characteristics can often provide reasonable surrogates. For example, areas with many renters can be targeted, but one cannot target renters individually for oversampling.
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Coverage Measurement in the 2010 Census Bureau also reconsider the metrics it uses to compare and assess 2010 CCM sample designs. In its simulations, the Census Bureau examined estimates of the coefficient of variation of estimates of net error, rate of erroneous enumerations, rate of omissions, and the rate of P-sample nonmatches. The Bureau also looked at coefficients of variation for net error estimates for groups of poststrata from 2000. The panel would like to suggest, in addition, the use of several additional types of metrics. Letting DSEi = the direct dual-systems estimate for an aggregate i (e.g., state by major demographic group), Ei = the E-sample total for an aggregate i, Pi = the P-sample total for an aggregate i, Ii = the number of imputations for an aggregate i, EEi = the number of erroneous enumerations for an aggregate i, and Mi = the number of matches for an aggregate i, the panel believes that the following metrics would provide more direct indication of the benefits of alternative CCM designs: The first metric is intended to be evaluated at the block cluster level (based on synthetic estimation), while the remaining two metrics are computed at the state level. The first metric, is a local undercount estimate since DSEi + Ii is similar to the dual-systems estimate and Ei + Ii is an estimate of the census count. The second metric, is a measure of the percent of erroneous enumerations. The third metric, is a measure of the percent of whole-person imputations. The last two metrics therefore assess the degree to which an area is encountering problems in enumeration. The goal then is to select a CCM sample design that produces estimates of these quantities at the indicated level that have substantially lower variances than those from the currently proposed design. Simulation studies of the design alternatives mentioned above, using these metrics, may identify designs that are nearly as effective as the Census Bureau’s current design at estimating net coverage error at the level of states and major demographic groups while increasing the number
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Coverage Measurement in the 2010 Census of sampled census coverage errors. The panel believes there still may be sufficient time to carry out this analysis. The panel’s suggestion that the Census Bureau consider additional oversampling of difficult-to-count housing units in the 2010 CCM design is incomplete without considering what data should be used in support of this effort. Certainly, the Census Bureau could continue to use census and A.C.E. data from 2000, as in the above simulations, possibly making some effort to better identify erroneous enumerations and omissions given the weakness of A.C.E. data for that purpose. However, that might be too time-intensive an activity as 2010 nears. Census, ACS, and StARS (see Chapter 3) data could also be used as the basis for an artificial population study, in which the components of census coverage error were “imposed” on the census enumerations. That is, statistical models using current best guesses for causal factors and their impact on coverage error could be developed, relating person, household, and contextual characteristics to probabilities of duplication, omission, and being counted in the wrong location. Then, a number of simulated censuses and PESs could be conducted, with people and housing units missed, duplicated, and counted in the wrong place with various probabilities. Erroneous enumerations, as defined here (which excludes duplications and enumerations in the wrong location), would be more difficult to incorporate in such a study since one does not have a base population to apply a model to. However, this component is likely the least important to address, and there may not be an effective causal model predicting which newborns are erroneously included in the census, which recent deaths are erroneously included, which visitors are included, and which fictitious individuals are included. If the suggested study is carried out, then, analyses in 2010 to identify which factors are and are not associated with various components of coverage error can be used to refine the models used for incorporating components of coverage error to better plan the coverage measurement data collection in 2020. Finally, a very serious complication in carrying out this research plan is that many of the most important predictive factors in statistical models of components of census coverage error will have to be indicator variables for the various census processes used in association with the enumeration of each housing unit or individual. (This requirement results from having a feedback loop that identifies census processes in need of modification.) However, the census processes are generally not represented on the standard census files or in A.C.E. in 2000. This lack strongly argues for the collection of a master trace sample (a sample of households for which the entire census procedural history is retained) in 2010 and that the designs of the CCM sample and the master trace sample be such that there is substantial overlap between them. For current work, and in the case that
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Coverage Measurement in the 2010 Census a master trace sample database is not constructed in 2010, the Census Bureau should determine how it can use census management information files to populate an analysis database that represents the components of census coverage error and as many as possible of the predictors discussed in Chapter 5. None of the approaches suggested here as to how to examine the optimal extent of oversampling problematic households is ideal, which is not surprising. The Census Bureau does not have good historic information on how coverage errors are related to census processes, which makes targeting the sample much harder and which makes simulating the situation harder as well. However, the Census Bureau has acquired a lot of information about the circumstances that cause some of the coverage errors and where those more problematic areas are located; those areas need to be oversampled to some extent. The coverage problems do change from census to census and some of the problematic areas are due to idiosyncrasies that appear for only a single census. Yet it is sensible to assume that much of the causal nature of coverage error is persistent across at least a few censuses, and that is what needs to be captured in the CCM survey. So focusing on areas with high proxy interview rates or high imputation rates in the previous census, on areas with a large percentage of vacation homes, or on areas with many small, multiunit housing units (though this has some difficult definitional and implementation aspects) is likely to be beneficial in the design of the 2010 CCM survey since such households have been and are likely to remain hard to count. Of course, over time, new problems will crop up, and old ones will be addressed, and so the process of census improvement will be a dynamic one. Given that the design of the 2010 CCM PES needs to target block groups that have a higher frequency of housing units that are vulnerable to census coverage error, the Census Bureau should give serious consideration to alternative designs that, without sacrificing much efficiency in estimating net coverage error, could provide a larger number of (anticipated to be) hard-to-enumerate households and individuals. Such a design would improve the estimation of parameters of the statistical models linking coverage error to census procedures. In particular, the Census Bureau should consider implementing a design that mixes a high proportion of cases selected using the current design with a smaller proportion of cases in hard-to-enumerate areas. This design could be assessed through simulation studies like those the Bureau has already used, supplemented by additional metrics suggested here. Recommendation 6: The Census Bureau should compare its sample design for the 2010 census coverage measurement postenumeration survey with alternative designs that give greater sampling prob-
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Coverage Measurement in the 2010 Census ability to housing units that are anticipated to be hard to enumerate. If an alternative design proves preferable for the joint goals of estimating component coverage error and net coverage error estimation, such a design should be used in place of the current sample design. LOGISTIC REGRESSION MODELS In the last few years the Census Bureau has devoted a considerable amount of its resources on coverage measurement research to improving the estimation of net coverage error in 2010, with a primary focus on developing two logistic regression models to replace poststratification to address correlation bias. Any small-area estimates of net coverage error will likely be based on these same logistic regression models, replacing the use of (so-called) synthetic estimation. Both poststrata and synthetic estimation were used in the coverage measurement programs in 1990 and in 2000, so the current plan is a substantial change to the estimation of net coverage error at the level of both large and small domains. Despite the new focus on estimating components of error, there remains good reasons for devoting considerable attention to the estimation of net error. First, given the focus in 2000 on net error estimation, the data available from A.C.E. are not directly useful as substitutes for the data on components of coverage error that will be collected in 2010. An important example of this is the different definitions of correct enumerations in 2000 and 2010, which suggests that the frequency of erroneous enumerations and omissions will likely be substantially less and of a somewhat different nature in 2010 than they were in 2000. As a result, any attempts to model the 2000 A.C.E. data without accounting for various differences between 2000 and 2010 will probably provide limited guidance for how to estimate components of coverage error in 2010. (However, we believe that some efforts in this direction are warranted.) Second, as argued in Mulry and Kostanich (2006), estimating net coverage error facilitates estimation of the number of census omissions. Therefore, some focus on estimation of net coverage error is justified.3 Third, as noted in Chapter 2, strong interest remains for many census data users in the assessment of net coverage error, in particular for demographic groups, but also for states and cities. 3 Although the Census Bureau will use estimates of net coverage error to develop estimates of the number of census omissions for domains that will support various tabulations, we hope that the Census Bureau will develop analytical models based on the P-sample individuals that are determined to be census omissions. The main disadvantage of doing this is that this analysis may miss the types of census omissions that are not captured in either the census or the P-sample, which are collectively estimated using the Census Bureau’s approach.
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Coverage Measurement in the 2010 Census The Census Bureau plans to use logistic regression for fitting the probability of match status for the P-sample and the probability of correct enumeration status for the E-sample. Logistic regression is more flexible than poststratification in terms of handling continuous predictor variables and selective use of interactions among predictor variables. This flexibility potentially allows inclusion of more predictor variables without increasing the variance of estimated probabilities. Furthermore, logistic regression is a model that, in this context, is applied at the level of the individual; therefore, information collected at that level can be easily used in conjunction with information that is collected at a more aggregate level. Finally, not only is logistic regression likely to be better than poststratification in estimating net coverage error for these reasons, but it is also much better suited for the analytic purposes of providing a better understanding of which factors are and are not related to net coverage error than poststratification. Poststratification is mentioned in the earliest literature advocating the use of dual-systems estimation (DSE) to measure populations (Sekar and Deming, 1949), and it has been used in the census since the 1980 postenumeration program to reduce correlation bias. Poststratification simply means that one partitions the CCM sample data into groups that are more homogeneous and then separately estimates the adjusted population counts within those poststrata.4 A perfect poststratification would partition the P-sample population and the E-sample population so that the underlying enumeration propensities for individuals in a poststratum were identical. However, this is unattainable and therefore the practical goal is to partition the sample cases so that individuals are more alike within a poststratum than individuals are from different poststrata. If this is accomplished, correlation bias should be reduced (see Kadane et al., 1999, for details). Poststratification also supports the use of synthetic estimation, which carries down adjustments to census counts to low geographic levels. Synthetic estimation makes use of coverage correction factors, 4 See Chapter 3 for definitions. Note that CE is defined consistent with the definition of a correct enumeration in A.C.E., that is, an enumeration that is located in the search area.
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Coverage Measurement in the 2010 Census which are applied to any subpopulation in a poststratum by multiplying the appropriate factor by the relevant subpopulation’s census count to produce the adjusted count for that subpopulation. To produce geographic estimates, which often requires adding subpopulations that belong to different poststrata, one simply sums the associated adjusted counts. Estimates of the variance of synthetic estimates for small domains are necessarily a combination of estimates of the variance of the coverage correction factors for the poststrata involved (depending on the domains) and a residual variation due to any unmodeled heterogeneity of the relevant subpopulations of interest within the required poststrata. The first component can be estimated by standard methods. However, estimation of the second variance component is more difficult. As mentioned above, although poststratification has the advantages of reducing correlation bias and supporting synthetic estimation, a major disadvantage is that, as applied by the Census Bureau, it allows only a relatively small number of factors to be included in the poststratification scheme (and in the resulting synthetic estimation). This limitation exists because the Census Bureau typically includes the full cross-classification of the factors used to define the poststrata, and, as a result, the individual poststrata quickly become very sparsely populated, despite the large sample size of the PES. Use of more poststratification factors, and therefore more poststrata, trades off greater homogeneity in each poststratum at the price of higher sampling variances for the coverage correction factors. Furthermore, the fact that the various poststrata generally share some characteristics with other poststrata (for instance, there are many poststrata for Hispanic women) is generally ignored in the associated estimation. As a result, there is a failure to pool information when it may be beneficial to do so. The alternative that is being planned for use by the Census Bureau in the 2010 CCM is logistic regression of both the binary match/nonmatch variable and the binary correct enumeration/not correct enumeration variable. Poststratification is a special case of logistic regression in this context in which the predictors of the logistic regression are indicator variables for membership in the categories defining the poststrata, and all interactions are included in the model. In theory, for the same reasons that logistic regression may be preferred to poststratification at the aggregate at which that analysis is carried out, small-area estimates that are based on the probabilities of match and correct enumeration status estimated using logistic regression could improve on those provided through synthetic estimation by effectively averaging over more of the data. In the following, a number of issues relevant to the use of logistic regression are raised and discussed, and a variety of suggestions are
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Coverage Measurement in the 2010 Census as the observed values, without any conditioning. This assumption is extremely unlikely to obtain in either missing data problem.) If the missing at random assumption is not considered reasonable, one could impute M by conditioning on various aspects of R (referred to as pattern-mixture models; for details, see Little, 1993). It would be valuable for the Census Bureau to assess its current imputation methods in its coverage measurement models for consistency with the above principles. As noted above, the logistic regression approach for modeling match status seems too focused on the P-file data, ignoring potentially useful information both in auxiliary data used in the matching algorithm and in the E-file. It may be that after this reconsideration, modest adjustments to the current procedures will provide a model for match status with smaller mean-squared error under a variety of realistic models for both the generation of data and missing values. The Census Bureau’s current imputation methodology, hot-deck imputation, works well in situations with limited covariate information. However, the difficulty in this approach is that dealing with more than a few covariates at a time compromises its ability to condition on all relevant variables. In contrast, parametric multiple imputation methods make better use of covariate information, and these methods can be used to estimate the contribution to variance as a result of the missing data. An example of this is IVEWARE (see, e.g., Raghunathan et al., 2002). Another question involves the role of imputation for missing census characteristics values. After estimating the logistic regression of M on X, imputations for missing census characteristics are needed to provide the predictors for input to the logistic regression models to estimate a match probability for these cases, through: as input into the small-domains estimation procedure to be used in 2010. Use of hot-deck imputation here is reasonable, but an alternative is to estimate this probability directly given the observed E-sample characteristics, This approach avoids the additional uncertainty from the imputation, and it should be straightforward to employ with the move to use of logistic regression. Finally we note that the coverage measurement data collected in 2010, in particular the various follow-up data collections that are typically carried out, could be used to validate the imputation models used, though the sparseness of these samples may make this of only limited utility.
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Coverage Measurement in the 2010 Census In summary, missing data methodology needs to be viewed in the context of the complete-data problem, file matching. As noted above: Imputation is only useful if it adds information to the logistic regression; otherwise cases can be dropped. Imputations should be multivariate in order to preserve associations between missing variables. Imputations should condition on predictive covariates. For example, imputations should condition on M if M is observed, and imputations should condition on potential covariate information from matches or potential matches from the E-file. Some form of weighting might be developed to reflect the strength of the potential matches. The Census Bureau could also consider parametric multiple imputation as an alternative to the hot deck because it makes better use of the covariate information and because it propagates imputation uncertainty. Finally, the Census Bureau could also consider nonignorable models, such as pattern-mixture models, if the missing-at-random assumption is likely to be violated. This is a set of research problems that the Census Bureau needs to allocate substantial staff resources to address. We believe that the benefits are likely to be considerable and the understanding from the P-sample matching problem discussed in detail should be transferable to some of the other missing data problems listed on p. 103. The Census Bureau should identify missing data methods that are consistent with the philosophy that is articulated above and implement those methods in support of statistical models of Census Coverage Measurement data in 2010. Recommendation 7: The Census Bureau should develop missing data techniques, in collaboration with external experts if needed, that preserve associations between imputed and observed variables, condition on variables that are predictive of the missing values, and incorporate imputation uncertainty into estimates of standard errors. These ideas should be utilized in modeling the census coverage measurement data collected in the 2010 census. MATCHING CASES WITH MINIMAL INFORMATION For an E-sample enumeration to have sufficient information for matching and follow-up, as defined in the 2000 census, it needed to include a person’s complete name and two other nonimputed characteristics. To be data defined in the census itself, an enumeration simply had to have two non-imputed characteristics. In the A.C.E. E-sample in 2000, 1.7 percent
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Coverage Measurement in the 2010 Census (4.8 million sample survey weighted) of the data-defined enumerations had insufficient information for matching and follow-up. These cases were coded as “KE” cases in A.C.E. processing. A.C.E. estimation treated KEs as having insufficient information for matching, and they were removed from the census enumerations prior to dual-systems computations. If KEs are similar in all important respects to census enumerations with sufficient information for matching, removal from dual-systems computations slightly increases the variance of the resulting estimates, but it does not greatly affect the estimates themselves. Removal of KEs helped to avoid counting people twice because matches for these cases are difficult to ascertain. Also, it was difficult to follow up these E-sample cases to determine their match status if they were initially not matched to the P-sample because of the lack of information about whom to interview. However, some unknown and possibly a large fraction of these cases were correct enumerations. Therefore, removing these cases from the matching inflated the estimate of erroneous enumerations, and it also inflated the estimate of the number of census omissions by about the same amount, since roughly the same number that are correct enumerations would have matched to P-sample enumerations. (There is no way of validating this assumption since the KEs generally cannot be followed up.) Given that the emphasis in 2000 was on the estimation of net census error, this inflation of the estimates of the rates of erroneous enumeration and omission was of only minor concern. However, with the new focus in 2010 on estimates of components of census coverage error, there is a greater need to find alternative methods for treating KE enumerations. One possibility that the Census Bureau has explored is whether many of these cases can be matched to the P-sample data using information from other household members. To examine this possibility, the Census Bureau carried out an analysis using 2000 census data on 13,360 unweighted data-defined census records with insufficient information for matching to determine whether their match status could be reliably determined. (For details, see Auer, 2004; Shoemaker, 2005.) This clerical operation used name, date of birth, household composition, address, and other characteristics to match the cases to the P-sample. For the 2000 A.C.E. data, 44 percent of the KE cases examined were determined to match to a person who lived at the same address on Census Day and was not otherwise counted, with either “high confidence” or “medium confidence” (which were reasonable and objectively defined categories of credibility). For the 2000 census, this would have reclassified more than 2 million census enumerations from erroneous to correct enumerations, as well as a similar number from P-sample omissions to matches, thereby greatly reducing the estimated number
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Coverage Measurement in the 2010 Census of census component coverage errors.11 (We note that it is important in carrying out this research to remain evenhanded in evaluating whether a case does or does match; this is not simply an effort to identify more cases that are matches.) The treatment of the KEs remaining after this revisiting of the definition of insufficient information for matching can be viewed as another component of “error” in the same way that a person incorrectly geocoded is an error—that is, as a problem for processing but not a part of what one would call an omission or an erroneous enumeration. Therefore, the use of the term “erroneous enumeration” for these cases is inappropriate. Cases with insufficient information should be treated as having unknown or uncertain enumeration or match status and the term “erroneous” should be reserved for incorrect enumerations. The terminology used needs to distinguish between types of error and the uncertainty associated with these types of error for particular cases. The panel is impressed with the findings of this research, which should substantially improve the assessment of components of census coverage error in 2010. In considering further development of the idea, it would be useful to try to find out more about any characteristics associated with KEs in order to find out how to reduce their occurrence in the first place. StARS might be useful for this purpose. Furthermore, the clerical operation used to determine the status of KEs was resource intensive, and it would be useful to try to automate some of the matching to reduce the size of this clerical operation in 2010. We anticipate that, as a result of this research, the Census Bureau will adopt a different standard of what is considered to be insufficient information for matching more generally. DEMOGRAPHIC ANALYSIS Demographic analysis may be facing a very dynamic period in the next few years for several reasons. First, nearly all record systems are becoming increasingly more complete with higher quality data. Second, the American Community Survey is now providing a great deal of useful, subnational information that could be used to improve and extend demographic analysis estimates. Third, StARS, a merged, unduplicated list of U.S. residents and addresses, is also a likely source of information on the number of housing units and residents at small levels of geographic aggregation that could also be used to improve demographic analysis estimates. 11 For the remaining unresolved cases, the Census Bureau currently plans to treat them in a separate category as “enumerations unable to evaluate.”
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Coverage Measurement in the 2010 Census At the same time, some things are becoming more complicated, notably, the expansion of the number of race and ethnicity categories on the decennial census and the growing and increasingly mobile population of undocumented immigrants. In this context, the panel was asked to examine how demographic analysis might function more effectively as an independent assessment of the quality of the coverage of the decennial census. In addition, the panel was asked to consider the use of sex ratios from demographic analysis, especially for Hispanic residents, to reduce the effect of correlation bias in dual-systems estimation. As described above, the basic demographic analysis equation is where represents the current estimate of the population for demographic group i and geographic area j, is the analogous estimate for a previous census, Bij represents the number of births between the current and a previous census, Dij represents the number of deaths between the current and a previous census, Iij represents the number of immigrants between the current and a previous census, and Eij represents the number of emigrants between the current and a previous census, all for demographic group i and geographic area j. Once is computed, the net census undercount, Ûij for demographic group i and area j is defined as where Cij is the census count, again for demographic group i and area j. Error is introduced into estimates from demographic analysis due to omissions in the birth and death records and due to large inaccuracies in the data on immigration and emigration. The error in net undercoverage estimates from demographic analysis then stems from error in the various components, error in the census counts, and any lack of alignment of the demographic categories. Given these concerns, the most reliable outputs from demographic analysis are any national counts by age and sex, and functions of such counts, in particular sex ratios by age; birth and death estimates; and historical patterns of various kinds. More problematic outputs are race (depending on the degree of alignment to the new race/ethnicity categories) and subnational estimates for demographic groups. The most problematic outputs are estimates of international migration components, estimates of the Hispanic population, subnational totals for states and smaller geographic areas. The Census Bureau plans for demographic analysis in 2010 are to produce “estimates” and “benchmarks,” with estimates represented to users as being more reliable than benchmarks. The Census Bureau will produce estimates of national level totals by year of age and by sex, and
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Coverage Measurement in the 2010 Census estimates of 2000–2010 change for the above groups. The Census Bureau will also produce benchmarks of national net undercount error by age, sex, and race/ethnicity. In addition, the demographic analysis program will produce sex ratios by age and race/ethnic origin, possibly for use in reducing the effects of correlation bias on estimates of net undercoverage from the census coverage measurement program. Even without any major advances from 2000, demographic analysis will still likely play an important role in evaluation of the 2010 census. As pointed out above, demographic analysis provided an early indication that the initial estimates of the total U.S. population from A.C.E. may have been too high, and it will continue to provide an estimated count that serves as a useful estimate for many demographic groups and a useful lower bound for others. The Census Bureau is currently pursuing important research directions, though it is unclear whether they will contribute to the 2010 demographic analysis program. Those research plans include: (1) improved estimation of international migration, (2) estimation of the uncertainty of demographic analysis estimates, and (3) progress towards the production of subnational estimates. The latter includes research on methods and data sources, with some pieces already considered of possibly acceptable quality, such as estimates of the number of people younger than 10 years of age at the state level. We believe that these are extremely important projects to pursue and deserve full support from the Census Bureau. In addition, the panel has the following questions concerning the 2010 demographic analysis estimates that may help orient these research avenues: Given that there is race/ethnicity incomparability between the decennial census and demographic analysis, which categories are going to be used in 2010? Given overlapping data for some cohorts (e.g., Medicare information for those over 65) in comparison with standard demographic analysis, which sources will be used and how will that be determined? Will there be efforts to combine information? Estimates of Hispanic origin were produced by the censuses of 1980, 1990, and 2000, as were adjusted counts. Have these sequences been examined to determine their likely quality over time? In considering subnational estimates, relatively high-quality estimates are available of the number of native-born children under 10 years old at the state level, and the number over 65 from Medicare, again at the state level. Given additional information on interstate migration from tax returns, school enrollment, and possibly the American Community Survey, could high-quality
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Coverage Measurement in the 2010 Census estimates be provided for the remaining demographic groups at the state level? If the Census Bureau again uses sex ratios from demographic analysis to reduce the correlation bias in adjusted population counts, should these be applied for all minority men or selectively, as in 2000? The American Community Survey is providing information that might be extremely useful for improving demographic analysis estimates. The possibilities include: (1) better estimates of the number of foreign-born residents, (2) better estimation of net international migration, and (3) information on sex ratios for more detailed ethnic and racial groups. How should each of these information sources be best used to improve demographic analysis, and what evaluations should be used to support decisions of implementation? Measurement of the size of the undocumented population is a continuing problem for demographic analysis. The current method, described in Passel (2005), is, roughly speaking, to subtract the estimated size of the legal immigrant population from the estimated size of the total foreign-born population. Are there any new methods that might be more effective in estimating the size of this population? StARS is already, or will soon be, of high enough quality to provide useful input into demographic analysis estimates. There are reasons to believe that administrative records could play an important role in improving various aspects of demographic analysis, especially the counting of immigration and emigration, and research in this area would be very desirable. Demographic Analysis in Combination with Dual-Systems Estimation As part of A.C.E. revision II, the Census Bureau decided to modify the final A.C.E. estimates based on sex ratios from demographic analysis and the assumption that the A.C.E. counts for women and children were correct. Specifically, at the level of aggregate poststrata (aggregated over nondemographic and geographic characteristics), the A.C.E. counts for black men 18 and over and for all other males 30 and over were adjusted upward so that the ratio of women to men for A.C.E. (essentially) agreed with that estimated using demographic analysis. The argument in support of this joint use of demographic analysis and dual-systems estimation is as follows. Demographers generally believe that the most accurate outputs of demographic analysis are national-level sex ratios by age for blacks and nonblacks. Even if absolute counts are subject to some bias, sex ratios are expected to be quite accurate.
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Coverage Measurement in the 2010 Census Historically, at least for adult blacks, the corresponding male-to-female ratios based on adjusted counts using dual-systems estimation have been lower than those from demographic analysis, suggesting that correlation bias (or other sources of bias) result in relative underestimation of adult males by dual-systems estimation. Because the most obvious source of correlation bias (heterogeneity of enumeration probabilities) would not have resulted in a negative bias for dual systems estimates, the most conservative step, in terms of additional counts, is to leave estimates for the female population unchanged and to increase the male population enough so that the resulting sex ratios for the adjusted counts agree with those from demographic analysis. It is not sufficient to simply add these additional enumerations at the level of the aggregate poststrata; they must then be allocated down to the poststrata within each of the aggregate poststrata. Bell (1993) and Bell et al. (1996) identified five different methods for doing so, but there is little evidence available as to which of the methods works best. The Census Bureau selected one of these five approaches on the basis of its best judgment, but the arbitrariness of the selection, along with the fact that the counts were sensitive to the method used, is troubling. Also, given the limitations of demographic analysis, this technique could not be applied to such particular subgroups as nonblack men aged 30 and over (especially Hispanics), despite some historical evidence that a similar correction might have improved estimates for those subgroups. Finally, adjusted counts for both adult males and females have rested on the assumption that there is no correlation bias for adult females. Admittedly, the approach used resulted in higher “face validity” for the adjusted census counts at the aggregate level as a result of the consistency with the sex ratios from demographic analysis. However, given the issues described above, especially the lack of a formal assessment of the effect of this process on the quality of the resulting counts, the decision was controversial. Given this situation, it seems reasonable to carry out a more comprehensive evaluation of what was done in 2000 and possible alternatives before adopting a similar modification in 2010. (The Census Bureau currently plans to use a similar technique in 2010 as a correction for correlation bias.) Artificial population studies, in which models are developed to designate which individuals in an artificial population are and are not missed by the census, the PES, and by the record systems used by demographic analysis could be useful in such evaluations. We suggest that the Census Bureau include the approach described by Elliott and Little (2000) in their analysis of the method used in 2000. Their approach provides useful smoothing to the technique described in Bell (1993) and Bell et al. (1996). In addition to the beneficial smoothing, Elliott and
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Coverage Measurement in the 2010 Census Little’s work provides estimates of precision that incorporate the uncertainty in the demographic analysis sex ratios. In addition, the information from the American Community Survey and from StARS on various demographic statistics, such as sex ratios, could be considered for use in providing not only modifications to the counts for males, but also modifications to the counts for females, avoiding the necessity of relying on the assumption that no correlation bias exists for that demographic group. Estimation of Uncertainty of Demographic Analysis The Census Bureau (see Robinson et al., 1993) conducted initial research on developing uncertainty intervals for population forecasts, but to date these have not been fully developed. Development of such uncertainty intervals would have two benefits: users would be supplied with uncertainty intervals with a formal probabilistic interpretation, and estimates from demographic analysis could be combined with estimates from independent sources by weighting by the precision of each estimate. In the past 15 years, a number of researchers have suggested interesting methods to consider for development of uncertainty intervals. Poole and Raftery (2000) suggest the use of Bayesian melding for this purpose. Briefly, the idea is that one has expert knowledge about inputs to a deterministic model and their variability (i.e., a prior distribution) and expert knowledge about the outputs of interest (the forecasts), which through exact or approximate inversion presents a second prior distribution for the inputs. These two prior distributions then have to be reconciled. There is also the most recent data for the inputs that have been collected, and one can develop likelihoods for the previous inputs and outputs given the data. Bayes rule is then used, implemented by the sampling-importance-resampling algorithm of Rubin (1988), to update the prior distribution to produce a posterior distribution of the forecasts, which would include a posterior variance. Other approaches have also been suggested by, among others, Alho and Spencer (1997) and Lee and Tuljapurkar (1994). Given all of this promising research, and the benefits from the development of uncertainty intervals, it would be valuable for the Census Bureau to revisit this issue and evaluate some of these approaches for their applicability to demographic analysis of the U.S. census. It is true that the U.S. census tends to have idiosyncratic challenges each decade, such as the number of undocumented immigrants that are enumerated in a given census, the number of duplicate enumerations from multiple modes of enumeration, or the degree of census undercoverage, and these challenges may be difficult to model. Therefore, in particular, the specific stochastic models suggested
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Coverage Measurement in the 2010 Census by Alho and Spencer (1997) and Lee and Tuljapurkar (1994) might need some modification. However, even recognizing this, if started now, the panel is confident that a research effort devoted to this issue would very likely produce useful uncertainty intervals for the 2010 census. In summary, demographic analysis played an important role in helping to evaluate the estimates produced by A.C.E. in 2000, and it can play an even larger role in 2010 and 2020, especially if some improvements are implemented. Those improvements include improving the measurement of undocumented and documented immigration, development of subnational geographic estimates, development of estimates of uncertainty, and further refining methods for combining demographic analysis and coverage measurement survey information. Recommendation 8: The Census Bureau should give priority to research on improving demographic analysis in the four areas: (1) improving the measurement of undocumented and documented immigrants, (2) development of subnational geographic estimates, (3) assessment of the uncertainty of estimates from demographic analysis, and (4) refining methods for combining estimates from demographic analysis and postenumeration survey data.
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